Servo-mechanism synchronizing system



A. ALFORD- ET AL SERVO-MECHANISM SYNCHRONIZING SYSTEM Filed May 24, 1946 IO n INVENTORS ANDREW ALFORD ERNEST o. BARKOFSKY ATTORNEY Aug. 9, 1949.

\Avu z v Patented Aug. 9, 1949 SERVO-MECHANISM smcnaomzmo SYSTEM Andrew Alford, Cambridge, bins and Ernest c. Barkofsky, Inyokern, Callil, assignors to the United States of America as represented by the Secretary of War Application May 24, 1946, Serial No. 672,026

1 Claim. 1

This invention relates generally to electrical apparatus, and, more particularly, to a method and means for synchronizing the transmitting (driving source) and receiving elements (driven load) in a synchro data-transmission system.

In many synchro systems, the transmitter synchro may be geared to the driving source and the receiver synchro may be geared to the driven load. When such gearing is in other than unity ratio, there will be several possible orientations oi the driven load for a given angular position of the driving source in which the synchro system will run in synchronism, in as much as the driving source may occupy any of several positions for a given position or the transmitting synchro.

It is, therefore, an object of the present inven tion to provide a means for accurately aligning the driving source and the driven load of a synchro data-transmission system.

It is another object of the present invention to provide an associated means for periodically checking the synchronization of such a system during operation.

Other objects, features, and advantages oi. this invention will suggest themselves to those skilled in the art, and will become apparent from the following description of the invention, taken in connection with the accompanying drawing, the single figure of which is a schematic diagram of one embodiment of the invention.

Referring now to the drawing, the embodiment shown forms a part of a radio communication system wherein a luminous line on an indicator such as a cathode ray tube screen rotates in synchronism with a rotating directional antenna.

An antenna drive motor 5 (driving source) has a field coil 8 and an armature 1, one terminal of each of which is connected to ground. A directional antenna III is mechanically coupled as indicated by dotted line ii to motor 5 in such a manner as to be driven in rotation by the motor.

Rotating antenna I is likewise mechanically coupled as indicated by dotted line I! through suitable gearing (not shown) to rotor coil ll of a transmitter synchro II. Electrically associated with transmitter synchro I is a receiver synchro II, the stator coils II and I! of the respective two synchros being electrically connected in the usual manner, and rotor 20 of receiver synchro I! being electrically connected to rotor l4 of transmitter synchro ii. A switch ii is provided in the rotor circuit to permit the circult to be opened during the process of syn chronizing the system.

Antenna drive motor 5 is provided with a D.-C. voltage from terminals 25, the negative terminal being grounded and the positive terminal being connected at junction 26 to the ungrounded terminal of motor field coil 6. A motor speed controlling variable resistance 21 has one terminal connected to junction 26 and the other terminal connected to a terminal 28 of an electromagnetic relay 30.

Relay 30, in its simplest form, comprises a coil 3i having terminals 32 and 33 and a movable arm 34 actuated by coil 3| as the coil is energized or de-energized as presently described. The above mentioned terminal 28 of the relay is connected to relay contact 35 while grounded relay terminal 36 is connected to relay contact 31.

Movable arm 34 is connected to the ungrounded terminal of motor armature l and in the position of the relay shown in the drawin establishes a motor driving circuit, the speed of the motor being controllable by variable resistance 21,

A rotatable commutator 40 is mechanically coupled as indicated by dotted line" torotatable antenna ii. The commutator has rotating electrically connected spaced elements 42 and correspondingly spaced stationary elements 43, the two pairs of elements registerring with each other at one angular position of the commutator. One stationary element 43 is grounded, and the other element 43 is connected to terminal 33 of relay coil 3|.

D.-C. voltage is applied to relay 30 by a connection 45 between the positive voltage terminal 25 and terminal 32 of relay coil 3i. Switch 46 is provided in this circuit to permit selective operation of the relay.

The receiver synchro I1 has its rotor 20 mechanically coupled through means 50 to indication positioning elements (not shown) of an indicator ii. The indicator 5i may be a cathode ray oscilloscope and, depending upon the type of cathode ray tube used, the indication positioning elements may be a movable electromagnetic beam positioning coil or a, sweep circuit for electrostatic beam positioning plates. A handwheel 52 is provided to actuate the indication positioning means independently of receiver synchro II.

An A.-C. voltage is applied to terminals 55, this voltage being connected across the rotor coils l4 and 20 of the transmitter and receiver s chros, respectively. By means of a tap 58 to resistor 51 connected across terminals 55', a portion of the applied A.-C'. voltage is impressed through a switch 58 on indicator 5| to cause an indication (luminous line) to appear on the indicator screen.

Operation of the system will now be described, the purpose being to achieve initial synchronization between the angular direction of rotatable antenna l and the indication (luminous line) appearing on indicator A pro-determined zero-reference position is selected, this position usually being north in the case of a ground system and in line with the axis of the airplane in case of an airborne system. A- suitable fixed marker is provided on the indicator to correspond with the pre-determined zero-reference position. Commutator 40 is so adjusted that movable elements 42 register and make contact with stationary elements 43 when antenna i0 is pointed in the zero-reference direction.

In utilizing the system to achieve initial synchronization, switch 2| in the rotor circuit of the synchros is placed in open position and switch 58 to the indicator is placed in closed position. Motor 5 is caused, by proper adjustment of resistance 21, to rotate slowly. Switch 46 in the relay circuit is then closed and when elements 42 and 43 of commutator 40 make contact, the relay circuit is established, coil 3| is energized and movable arm 34 is moved against contact 31. This short-circuits the motor to ground with the result thatthe motor then functions as a magnetic-brake to fixedly position antenna ill in the predetermined zero-reference direction.

Handwheel 52 is then actuated and the indication (caused by the A.-C. voltage applied at terminals 55) on the indicator screen is moved until it coincides with the zero-reference mark on the screen. The system is now in initial synchronization and switch 2| may now be closed to place the A.-C. voltage across the rotor coils of the synchros. Switches 58 and 46 may now be opened, the opening of switch 46 causin de-energization of relay 30 whereupon movable arm 34 makes its normal connection with contact 35. This establishes the operating circuit to'motor 5 and motor operation is resumed, the speed being regulated as desired by resistance 27. The above procedure insures that the antenna I0 and the indication on indicator 5| start in syncronism.

I As there is always the possibility that the system may slip out of synchronism, during operation, an

associated means is provided to permit periodic checks during system operation. A second source of A.-C. voltage is applied to terminals 60, one terminal of which is grounded. The other terminal is connected to the indicator through resistance 6|, normally open switch 62, capacitance 63 and conductor 64. Grounded resistance 65 is connected to conductor 64 to complete the circuit to ground.

To make a synchronization check of the system during operation, switch 62 is closed. Thus a signal will appear on the screen of indicator 5|. When the antenna rotates to the zero-reference position, elements 42 and 43 of commutator 40 register to ground the signal applied at terminals 60. This causes the indication to disappear from the screen of indicator 5|, and if the signal disappears right at the zero-reference position as indicated by the fixed marker, the system is in synchronization. If it disappears at anyother position on the indicator, the system has slipped out of synchronization and it may be re-synchronized in accordance with the steps described above.

What is claimed is:

In a synchro data-transmission system having a driving source, an element mechanically coupled thereto and driven thereby, a transmitter synchro geared to said element to rotate said element at any speed but an integral-multiple of the speed of rotation of the said synchro and driven thereby, a receiver synchro electrically connected to said transmitter synchro, and an indicator, said indicator providing a mark indication in the ratio of said element to said transmitter synchro and having means mechanically associated with said receiver synchro for continuously positioning said mark in accordance with the position of said receiver synchro, a means for achieving initial synchronization between the angular position of said driven element and the position of said indication mark comprising means responsive to the positioning of said element at a predetermined reference direction for stopping said driving source when said element is aligned in a predetermined direction, means for opening the electrical circuit between the rotors of said transmitter and receiver synchros and means for rotating said receiver synchro until said mark is aligned with a reference mark on said indicator.

ANDREW ALFORD. ERNEST C. BARKOFSKY.

REFERENCES (CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

